The “open time” of emulsion paint is the time interval during which freshly applied paint can be blended with subsequently applied paint without the appearance of lack of uniformity. Under one approach, open time can be extended by adding volatile organic compounds (VOC) such as glycols into the emulsion paint formulation. However, environmental regulations limit the level of VOCs in paint compositions. In response to such regulations, low VOC aqueous paints have been developed as an alternative to environmentally unfriendly VOC solvent-based paints.
Currently, in many low VOC aqueous paints, open time becomes unacceptably short, especially under fast dry conditions such as low humidity and high temperature. Open time problems include, but are not limited to, skinning of left-open paints, not being able to cut back or blend in during brushing and rolling, and non-uniformity of sprayed surfaces.
Some attempts involve modifying the aqueous paint composition during the manufacturing process. For example, U.S. Pat. No. 5,270,380 is related to a method for forming an aqueous coating by combining a latex polymer and modifying compound having complementary reactable groups. Similarly, U.S. Pat. No. 6,303,189 describes methods where the improvement in open time results from the addition of an aqueous polyurethane dispersion to an aqueous coating composition having at least one-film forming latex polymer.
U.S. Pat. No. 7,071,261 relates to aqueous paint compositions comprising a dispersion of polymeric nanoparticles with a mean diameter of 1 to 50 nanometers, which improves open time. However, the polymeric nanoparticles also include amine functionality and at least one multi-ethylenically-unsaturated monomer.
Another method of improving open time involves the use of a paint extender, which a consumer can add to a pre-manufactured aqueous paint. One latex-based paint extender on the market is Floetrol®, which is commercially available from the Flood Company of Hudson, Ohio. However, when Floetrol® is added to paints, the aqueous paints still tend to form skins, which are indicative of poor open time. Floetrol® also negatively affects water sensitivity and paint flow leveling. Furthermore, Floetrolt® also does not provide compatibility with many commercial low-VOC latex paints since it causes quick syneresis and separation. Floetrol® also reduces the gloss of higher sheen paints, such as semigloss and high gloss paints.
Thus, there remains a need for a latex-based paint extender for low-VOC aqueous paints that overcome the aforementioned limitations of the prior art.